One transmission technology supporting backbone networks of optical communication is OTN (Optical Transport Network) standardized by the ITU-T (International Telecommunication Union Telecommunication Standardization Sector).
The OTN is a technique for encapsulating client signals of SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy), Ethernet (registered trademark), or the like, to thereby generate a frame having a hierarchical structure and providing data transmission suitable for WDM (Wavelength Division Multiplexing).
As a conventional technique, there has been proposed a technique of adding synchronization information by inverting predetermined bits of reserved bits (Japanese Laid-open Patent Publication No. 03-201837). Another proposed technique is to use a reserved byte as an identifier for phase adjustment (Japanese Laid-open Patent Publication No. 2004-266480).
Overhead of an OPU (Optical Channel Payload Unit) frame, which is an element of an electrical layer of the OTN, includes a field called PSI (Payload Structure Identifier) indicating information on client signals mapped into a payload area of the OPU frame. The PSI is transmitted with a period of 256 frames.
In the case where a change is made to a payload structure of the OPU at a transmitting end, the PSI is also changed according to the changed payload structure and then transmitted. In this case, a receiving end accepts a new value of the PSI, transmitted with a period of 256 frames, after having received the changed PSI three times in succession.
As a result, it takes a period of time corresponding to up to 768(=256×3) frames from the change to the OPU payload structure at the transmitting end to the acceptance of the new PSI value at the receiving end.
Thus, according to the conventional OTN frame transmission scheme, in the event of a change to information on the payload structure, it takes time for the changed information to be reflected at the receiving end, resulting in a reduction in transmission quality.